1. Field of the Invention
The present invention relates to a method for preparing hydrazodicarbonamide (HDCA) using biuret as a starting material, and more particularly, to a more economical and efficient method for preparing HDCA than the method described in Korean Patent application No. 2000-691 of the present inventors.
2. Backgrounds of the Invention
Hydrazodicarbonamide (HDCA) is a useful compound as a source material for producing azodicarbonamide which is one of the world-widely used foaming agents. As shown in the following Reaction equation 1, azodicarbonamide (2) can be obtained by oxidizing hydrazodicarbonamide (1) with an appropriate oxidizing agent.

Conventional methods for preparing HDCA includes (i) a method of reacting 2 moles of urea with hydrazine which is produced by Raschig process or derived from ketazine, (ii) a method of reacting 2 moles of urea with hydrazine which is derived from urea (Urea Process), (iii) a method of reacting 1 mole of urea with semicarbazide which is produced by reacting sodium hypochlorite, urea and ammonia, and (iv) a method of using biuret as a starting material. However, the methods (i) and (iii) which use hydrazine or semicarbazide and the method (ii) have drawbacks such as a complicated reaction process, a low yield, a high raw material cost, and a long reaction time. Furthermore, the above-described methods are environmentally undesirable since the large quantities of the raw materials are required to produce HDCA.
To overcome these drawbacks, the present inventors have proposed a method for synthesizing HDCA using biuret as a starting material (See Korean Patent application No. 2000-691), and the method is shown in the following Reaction equation 2.
wherein, M is a metal and X is a halogen. As shown in reaction equation 2, Korean Patent application No. 2000-691 discloses the method for preparing HDCA comprising the steps of (i) reacting biuret with metal hypohalogen or halogen/base to obtain metal monohalobiuret salt, and (ii) reacting the obtained metal monohalobiuret salt with ammonia to produce HDCA. However, in order to produce HDCA in industrially preferable yield with the above described method, a metal compound catalyst such as sulfates, chlorides, carbonates or hydroxides of amphoteric metal or alkali metal, or an inorganic acid catalyst such as hydrochloric acid, sulfuric acid or nitric acid are required in the amount of more than 0.05 moles with respect to 1 mole of monohalobiuret. Therefore, this method has drawbacks in that it requires high catalyst cost and the cost for after-treatment of the produced HDCA due to the large amount of the residual catalyst, and the method is also environmentally undesirable. In addition, the reaction rate and yield are not sufficiently high even when these catalysts are used.